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Ian Tse's M.S. thesis: Fluid shear influences on hydraulic flocculation systems characterized using a newly developed method for quantitative analysis of flocculation performance is the definitive document as of the summer of 2009 on tube flocculation and FReTA. Some of the child pages here appear to be out of date. (Please revise this first part ASAP. These comments have not been changed since August.)
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The goal of any flocculation process is to transform suspended colloidal particles into flocs that can be removed by sedimentation. The design of sedimentation tanks is dictated by the settling velocity of the flocs. Floc capture requires that the fluid residence time in a sedimentation tank or in plate or tube settlers be greater than the time required for the flocs to settle out. (Not necessarily. Not all flocs have to settle out and the fluid residence time may or may not affect how and when the floc particles settle out.) Therefore, one design goal of flocculators is to create flocs with sufficiently high sedimentation velocities. Unfortunately, guidelines for proper design and operation of hydraulic flocculators are incomplete. The appropriate energy dissipation rate required at different points along the flocculator that will produce the best flocs (what do you mean by "best"?) is not well understood. It is expected that high energy dissipation rates will initially enhance the collision frequency of small particles creating larger floc aggregates, however high energy dissipation rates are also likely to cause break up of large flocs.
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